The invention relates to tunable acoustic systems including resonator port structure, adaptive passive control, and passive and active combinations.
The invention arose during continuing development efforts relating to the subject matter of U.S. Pat. Nos. 4,665,549, 4,677,676, 4,677,677, 5,044,464, 5,088,575, 5,216,721, 5,216,722, 5,418,873, 5,420,932, 5,446,249, 5,513,266, 5,541,373, allowed application Ser. No. 08/273,919, filed Jul. 12, 1994, allowed application Ser. No. 08/322,585, filed Oct. 13, 1994, allowed application Ser. No. 08/368,920, filed Jan. 5, 1995, allowed application Ser. No. 08/355,456, filed Nov. 7, 1994, all incorporated herein by reference.
Acoustic resonators are known in the prior art. An acoustic resonator typically includes a resonator cavity having a resonator port communicating with an exhaust flow passage such as a duct or other outside space conducting acoustic waves therethrough. For example, the classical Helmholtz resonator comprises an air cavity coupled to the outside space through some form of opening such as an orifice, slot, tube, or the like. Such resonators are effective in reducing tonal noise over a narrow frequency band. The range of application of such silencers can be broadened by varying the acoustic impedance of the resonator to include additional tuned resonant frequencies. The resonant frequency can be varied by varying the volume of the resonator cavity and/or the area of the resonator port and/or the length of the resonator port.
The present invention provides simple and effective adjustable port structure varying acoustic impedance of the resonator port. The invention also provides adaptive passive systems. The invention further provides passive and active combinations. The latter are particularly desirable in applications where it is desired to reduce noise level prior to active attenuation, and to use the ability of the active portion of the system to do broadband control.